This invention relates in general to microelectromechanical devices, and in particular to a microvalve device having a micromachined structure suitable for use in such devices as pressure regulating microvalve and a proportionally controlled microvalve.
MEMS (MicroElectroMechanical Systems) is a class of systems that are physically small, having features with sizes in the micrometer range. The scope of the invention is not limited by the way in which the system is produced. These systems may have both electrical and mechanical components. The term xe2x80x9cmicromachiningxe2x80x9d is commonly understood to mean the production of three-dimensional structures and moving parts of MEMS devices. MEMS originally used modified integrated circuit (computer chip) fabrication techniques (such as chemical etching) and materials (such as silicon semiconductor material) to micromachine these very small mechanical devices. Today there are many more micromachining techniques and materials available. The term xe2x80x9cmicrovalvexe2x80x9d as used in this application means a valve having features with sizes in the micrometer range, and thus by definition is at least partially formed by micromachining. The term xe2x80x9cmicrovalve devicexe2x80x9d as used in this application means a device that includes a microvalve, and that may include other components. It should be noted that if components other than a microvalve are included in the microvalve device, these other components may be micromachined components or macro sized (larger) components.
Various microvalve devices have been proposed for controlling fluid flow within a fluid circuit. A typical microvalve device includes a displaceable member movably supported by a body and operatively coupled to an actuator for movement between a closed position and a fully open position. When placed in the closed position, the displaceable member blocks or closes a first fluid port that is placed in fluid communication with a second fluid port, thereby preventing fluid from flowing between the fluid ports. When the displaceable member moves from the closed position to the fully open position, fluid is increasingly allowed to flow between the fluid ports.
A typical microvalve device also typically includes a spring element that urges the displaceable member toward one of the open position (in a normally open microvalve) or the closed position (in a normally closed microvalve). The spring element may be separate from the displaceable member, or may be an integral part of the displaceable member which is distorted under the urging of the actuator, with the distorted portion developing a force resisting the actuator and urging the displaceable member back toward the position in which the spring element is undistorted (or is least distorted). For example, U.S. Pat. No. 4,821,997 to Zdeblick describes a type of microvalve in which the actuator for the displaceable member consists of a fluid with a sealed cavity having a thin wall. When the fluid is heated, the fluid expands, and the thin wall bulges outwardly. The thin wall is disposed adjacent a valve seat in a fluid passageway, and, as the wall is distorted toward the valve seat, controls the flow of a fluid through the valve seat. The wall also acts as a spring element, due to it""s elastic deformation, developing a force urging the wall back toward its undistorted (non-bulging) position.
In operation, the actuator forces the displaceable member to move toward the position opposite to the position the spring element is urging the displaceable member toward. The actuator must generate a force sufficient to overcome the spring force associated with the displaceable member. As a general rule, the output force required by the actuator to move the displaceable member against the spring element increases as the displacement of the displaceable member increases.
In addition to generating a force sufficient to overcome the spring force associated with the spring element, the actuator must generate a force capable of overcoming the fluid flow forces acting on the displaceable member that oppose the intended displacement of the displaceable member. These fluid flow forces generally increase as the flow rate through the fluid ports increases.
As such, the output force requirement of the actuator and in turn the size of the actuator and the power required to drive the actuator generally must increase as the displacement requirement of the displaceable member increases and/or as the flow rate requirement through the fluid ports increases.
Accordingly, there is a need for a microvalve device capable of controlling relatively large flow rates and/or having a displaceable member capable of relatively large displacements with a relatively compact and low powered actuator.
The apparatus of the invention includes a microvalve device having a first plate, a second plate and a third plate. The second plate is connected between the first plate and the third plate. The second plate contains a stationary element and a moveable plate valve slider element. The slider element variably restricts the flow of a fluid through the microvalve device. The second plate defines a first supply port, an output conduit, and a return port. In a pressure increase position, the slider element allows the fluid to flow from the first supply port to the output conduit. In a pressure hold position, the slider element isolates the output conduit from both the first supply port and the return port. The pressure decrease position allows fluid to flow from the output conduit to the return port. Pressure from the output conduit acts against a first axial end face of the slider element. Preferably, a buffer piston extends axially from the first axial end face to dampen movement of the slider element and to act as a bearing to laterally support the slider element. In a pressure regulating valve embodiment of the microvalve device, the second axial end face of the slider element (opposite the first axial end face) is acted upon by a spring, with the position of the slider element being determined by a balancing of the force exerted by the spring and the force exerted by the fluid acting against the first axial end face. In a proportional microvalve embodiment of the microvalve device, the second axial end face of the slider element (opposite the first axial end face) is acted upon by pressurized fluid in a control chamber, with the position of the slider element being determined by a balancing of the force exerted by the fluid acting against the first axial end face and the force exerted by the fluid acting against the second axial end face. The pressure in the control chamber is preferably controlled by a pilot microvalve, so that the slider element forms a pilot operated microvalve.